Riding lawn mower



FIG. 1 is a front view of a riding lawn mower showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is an upper right front perspective view thereof.

The portions of the riding lawn mower shown in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a riding lawn mower, as shown and described. 